Method of heating and cooling at high temperatures



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IETHOD OF HEATING AND COOLINGv AT HIGH TEIIYERAIURES 2 Sheets-Sheet Z u,

Filed April 2o. 1922 Patented Mar. l, 192,7.

UNITED STATES PATENT OFFICE.

CROSBY FIELD, F YONKERS, NEW YORK, ASSIGNOR TO CHEMICAL MACHINERY COR-POB/ATION, A CORPORATION OF NEW YORK.

METHOD OF HEATING AND COOLING AT HIGH TEMPERATURES.

Application ltiled April 20, 1922. Serial No. 555,657.

My present invention is more or less closely densed. My inventionincludes various ways related to certain heat transferring operaofmaintaining a body of liquid 1n heat ab- 65 tions of the kind describedin my prior Patent N o.1,403,471, granted Jan. 10, 1922, and

6 application Serial Number 553,640, filed April 17, 1922. 1n thepresent case the heat transferring medium is a liquid ot boiling pointmuch above that of water, preferably mercury; the temperatures at whichheat is l0 to b e transferred are usually `far above said boiling pointof Water; the temperatures of heat transfer either toithe transferringniesures at the boiling or the condensing points,

or both; and these pressures may be controlled either by handmanipulation or automatic action ot valves, pumps or other suitablepressure-controlling devices.

While the system may be employed partly or exclusivelyfor cooling, theprimary purpose illustrated is heating substances, for distillation,sublimation or chemical reaction which require limiting the temperaturesfor a predetermined maximum or minimum, or-

between a. maximum and a minimum; or for different temperaturessuccessively.

ln certain cases the desired operation is continuously endothermic orheat absorbing. ln such cases the heating is by the condensation portionof the cycle and temperature control is accomplished by control. ot thepressure of the vaporbeing condensed.

An important feature of my invention concerns a system'which Willautomatically control the temperature of a desired region when theoperation in 'said region requires heating at one time and cooling atanother time under conditions where the operation of the-fluid mediummust include not only a primary conditionof condensing to impart heat,but also a secondary'condition of boiling to absorb heat.

Hence my invention concerns maintaining a body ofliquid medium in heatabsorbing relation to the region which is initially heated bycondensation of the heated vapor.

Preferably this'body of liquid is hot con- I densate which, instead ofbeing allowed to freely escape from the condensing region, is

several ways.

sorbing relation to the container.

Such body of liquid is of advantage in So longr as the material ormixture being heated is very much cooler than the condensate, thecondensate continues to serve as a heating medium by simple conductionof heat to the material through the Walls ofthe container. When thematerial or mixture has attained a steady teinperature approaching thatof the condensate,

the lat-ter is in position to serve as a regulating medium by absorbingheat. This may be beneficial even for purely endothermicor hea-tabsorbing operations Where the vaporized `heating medium is super-heatedpur- 7 posely, or accidentally, as where the level of the liquid mercuryin the boiler gets low; c

stance or an ingredient of a mixture being] so charged into thecontainer is at an undesirably-high temperature; `also Where thelchargebeing introduced includes elements likely tov evolve heat in a manneranalogous to the evolution of heat when sulphuric acid and Water aremixed. It is even more beneficial where exothermic reactions are likelyto occuraccidentally as by reason of impurities in the mixture or wherethe desired operation is being conducted at a temperature quite 90lclose to one which will precipitate an undesired exotliermic reaction;also wherethe purpose of the heating -is to induce an exothermicreaction which is'desired.

In all of these cases the heat imparting operation by condensationofheated vapor andthe heat absorbing operation by boiling ofi". thecondensate will come into effect auto'- matically by various intentionalor accidental changes of relative temperatures orloo i pressures. v l

Where the heating is for the express purpose of producing a-desiredexothermic reaction. the heat transferring Wall may be of thin sheetsteel so that the temperature drop between exterior and interior issmall. In-

held in heat. absorbing relation to the lower part ofthe container onWhich it was contemperature o for.

such case, the primary condition of condensing hot, vapor to reach 4 thedesired critical producing the eXotherm-ie reaction, and thesecondarycondition ot' boilingoff p l generated, will take elfect successivelyand automatically upon change ofV a few degrees in ythe temperature ofthe mixture..

The above and other features of my invention will be more evidentlfromthe following description in connection with the accompanying drawings,in which- Figs. 1, 2, 3, 4,'and arediagrammalic views of systems Figs. 1and 2a are detail views, showing in e'nd elevation, the heatingcondenser coils of Figs. 1 and 2, respectively. l

Fig. 4 is a Vcross sectional view 4on the line l1-J1, Fig. 4. i

In these drawings the boiler, pipes, valves, pumps, condensers, etc.,are cally indicated. These and all other parts likely to contact withmercury are preterably of iron or steel, since iron and steel areordinarily not attacked or even wetted by mercury. The various'containers and pipes for performance of the heating function areunderstood to be properly heat insulated.

In Figs. 1 and 2 the systems comprise similar elements but theirarrangement is diiierent in severalimportant particulars. In both ofthem there is a heat'absorbing and mercury boiling element which, in'this case, is a boiler 1, connecting through pipe 2 with condensing orheat-imparting coils 3, in contact with a cooling medium 4 in a suitablecontainer 5. In this casethe cool-.

ing medium is usually a compound or mixture of compounds to be heatedfor the purpose of causing distillation or sublimation or chemicalreaction or all three, either simultaneously or successively.

The container 5 may be of any desired metal suitable for its purposesince the mercury does not come in contact with it. As shown it ishermetically closed by a top 6 communicating through a pipe 7 with theusual vacuumizing pump and cooling chamber not shown. These parts may bethe ordinary vacuum distilling or sublimat ing unit, such as commonlyemployed in the manufacture of petroleum and coal tar products; and theusual mechanical stirring means (not shown) may be employed if desired.

lVhile the mercury boiling element 1 may be usefully employed as arefrigerating element for any desired heat evolving system', it is shownin this ease as being heated from any desired source, as for instance,furnace 1a, heated by oil or gas burner l".

- A vacuum pump applies suction through pipe 8 to the upper part of tank9 containing a body of mercury 10. The entire tank condensate to absorbthe heat so 4 bottomot the embodied in my invention.`

d1agrammati-- asiatica 9 serves as a mercury vapor condenser which maybe cooled merely by the surroundingA air as indicated 4in the drawing;or by a water jacket commonly employed for such purposes. The body ofmercury 10 serves as a. gas trap and mercury balance through `pipe 1l,which connects with the interior` of primary or main condenser coils 2S.The lower endet' 11 discharges at 12, vnear the body of mercury.Condens-ate can fall and air audf gases can be sucked oft withoutVadmitting outside air into the system. IDuring out-flow ot gases orvapor, whether byl excess pressurefrom the'boiler or'by suction vfromthe vacuum pump, the

level of the mercury` will be depressed to Y the mouth 12 of pipe- 11,as indicated in Fig. 2, but incase of reversal ot pressure as duringperiods of non-operation, theme17- cury will rise in tube 11, asindicated in Fig. 1. Preferably'the lheight of` tube 11 is at least 30inches, so that a complete vacuum in the heating system, accompanied bya normal atmospheric pressure in 9, will be in sufficient to cause'Areverse flow, either of mercuryor outside gases, into the mercury vaporsystem.

The condensing` coils 3 will be recognized as being similar in shape andstructure to the socalled coils commonly employed as radiators in dryingovens and tor steam heating generally. The socalled coils are reallyparallehJ-shaped, tubes connecting parallel headers St, 3*.

In both Figs. 1 and 2, condensed mercury is trapped in the curl of theJ-shaped tubes and mercury so trapped will be in heat absorbing relationto the material which is being heated by the mercury vapor in -thestraight parts of the tubes 3.

rThe principal differences between Figs. 1 and 2 are that in Fig. 1 thecurl ot' the condenser coils or tubes 3 is inverted; the pipe 2 from themercury boiler 1 is con nected to the lower cross pipe or header 3b, sothat tubes 3 operate as an up-flow condenser and the condensate drainsby gravity back through the lower header 3, and through vapor supplypipe 2 into the top of boiler 1; said boiler is at a low level, topermit such gravity drainage; and the liquid mercury retained in thecondenser in heat absorbing relation is that trapped in the upper curlof the tubes il and in the upper header 3a.

In Fig. 1 the level ot' the `liquid mercury in the boiler is indicatedby boiler 1 is on a much higher level so thatdotted line 46a-46a.

- below In Figs 1 and 2 the temperature oi the operation can becontrolled by controlling vthe internal pressure and as mostvconimercial operations on organic compounds will be 3570 centigrade,the boiling point of mercury at atmosphere, the working pressures willbe below7 atmosphere and can be controlledby a vacuum pump as indicated.

It will be understood that pressure gauges Ion the boiler, container andcondensing tank,

as Well as hand or automatic regulating devices t'or the vacuum pumps,maybe employed.

Fig. 3 shows another system in whicha body of condensate may be retainedin bathing contact with the container that is being heated by themercury vapor. system includes elements functionally similar to thesystem of Fig. 2. There is a mercury boiler 101 and furnace 101a heatedby gas or oil jet 101", the products of combustion being dischargedthrough stack 101. The hot mercury vapor flows through pipe 102 tocondenser 103 in heating relation to container 105 and mixture 104. 'Ihecondensed mercury flows by gravity through pipe 112 back to boiler 101,entering below `the level of the liquid mercurytherein. The system isvacuumized by vacuum pump 108, applyingsuction to pipe 108 in the upperpart ot tank 109, containing a body ot mercury 110 and thence throughpipe 111 Which communicates with the upper part ot the condenser jacket103. These parts may be the same as corresponding parts in Fig. 2. Thereis a water jacket 109asupplied with water through pipes 1091, 109C, forcooling the tank 109; also pipe 109r1 for drawing of mercury from saidtank. condenser 103 is in the form of an external jacket applying hotmercury vapor to the exterior ot' container 105. Other features notshown in Fig. 2 which are shown in Fig. 3 are valve 102, for controllingthe mercury vapor supply pipe 102; valve 11.2a for controlling theliquid mercury return pipe 112;

valve 111a for controlling the vapor exhaust pipe 111; and super-heatingcoil 101X which may be used to super-heat the mercury vapor supply topipe 102.

Said super-heater 101x is sometimes designed and operated torsuper-heating the mercury vapor enough to make up for heat losses inpipe 102 so that the said vapor In Fig. 3 the.

ing heat and boiling off as above explained.

In Fig. 3 this is accomplished either by adjusting'valve 112*L tothrottle the return flow of condensate or by arranging the boiler so theliquid level will be above the level of the bottom ott-entamer 105 asinFig. 2. Additional features shown in Fig. 3 are the pipe 102bvcontrolled by valve 102, which may be used to short circuit thesuperheater; also the slight pressure gauge 113 on boiler 101 and athermometer 114 projecting into the mixture 104.

. In the. system of Fig. 3, the primary control of the temperature is bycontrolling the internal pressures, thereby determining the boiling andcondensing points of the' mercury. The internal pressures are controlledfor below-atmosphere pressures through control of vacuum pump 108"7 alsoby hand i regulation of valve 111aL through which the pumpcommunicates'lwith the condenser: also by regulation of valve 102nwhereby the back pressure and boiling point in the boiler 101 may bevaried independently of the vacuum in the condenser jacket; also bycutting out or cutting in the super-heating coil 101". For most purposesthe internal pressures are all below atmospheric, but the valves affordmeans for making them anything desired, either below'or aboveatmosphere. y

In Fig. 4 the boiler 201 is upright, and has projections 201d and afiller piece 201e affording independent paths for vertical flow of theboiling mercury. It is heated in `furnace 201a by oil or gas jet 201band the furnace has a .smoke stack 201C. The mercury vapor flows throughpipe 202 into condenser jacket 203 in operative relation .to container205. The condensate returns to the vbottom of the boiler through 212while gases and surplus vapor may escape through pipe 211. controlled bypressure relie]c valve 230 adjustable for venting` at pressures above orbelow atmosphere by adjustment of weight 231. Pipe 211 is vacuumized bypump 208 `through pipe 208, and doWn-low condenser 200. Condensatereturns through pipe 209b and through check valve 200c to pi e 212 andthrough it to the boiler.

l`he height ot the boileris such that any desiredl depth of liquidmercury may be maintained in the condensing jacket by simply. chargingthe boiler to various heights. The upper unfilled part of the 3;namely', arm-inging so that the normal level of the mercury issubstantially above the same manner as the bottom ot the container' 205,so thatthe lower portion otl said c-ontaineris continuously bathed in abody of liquid mercury. In normal operation, this mercury will be hotcondensate which may be at or near the temperature of condensationasdetermined by the particular internal pressure then being maintained bythe pressure-regulating valve 230'. This body of condensate in the`iacket is' in an important strategic position in several particulars.

In case ot ordinary work'requiring only endothermic or heat absorbingoperations on the material 204, the condensed mercury is free to flowdownward through 212 and back to the boiler 201.

. But in cases where the reaction in material 204 becomes exothermic orheat generating, this mercury automatically begins'to function as acooling medium. It absorbs heat from the container 205 and begins toboil as soon as the temperature of the mixture 204 rises slightly abovethe critical condensing temperature as determined by the pressurecontrolling devices. The boiled olf liquid is replenished through pipe212 in` the boiler 201. The vapor resulting from 'the boiling has a freepath of escape through the regular vapor outlet 211 to condenser 209.Obviously the adjustment of the pressure relief valve may b e 'changedif it is desired to conduct the heat generating reaction at a diierenttemperature from that 'which initiated it.

Moreover where said reaction may be desrably continued at a highertemperature requiring a higher internal pressure of the mercury vaporthe sudden and great increase in the total volume of va r due to thejacket vbecoming a mercury oiling instead of a mercury condensing devicemay be taken advantage of to cause control to shift to a pressure reliefvalve -set or a higher pressure and temperature than the one whichcontrols the initial heating.

For this purpose and for purposes of safety in'general, I may employ arelief valve adapted to shunt the mercury vapor through pipe240 to thecondenser 209. Automatic means Jfor controlling this shunt arediagrammatically indicated as comprising a cylinder 250, containingpiston 251 adapted to be actuated downward by en cess pressures throughpipe 252 communi*-` cating with pipe 202. The piston may be adjustablycounter-balanced to operate at a desired pressure by means of weight 253on crease of pressurefm pipe `202,

1,e19,eea

Apipe 252 and atmosphere or between pipe 252and the shunt pipe 240.Sudden inas where the reactions in 205 become exothermic, will `forcepiston 251V downward opening by-pass nvalve`255. If desired, the samep1ston movement may operate through link 256 to close valve 257 in pipe202. Such openings and closings may be alternating according toconditions and may be partial or complete.

In Figure 5, the extends from below' the mercury indicated byline 47,well above the higher level in 47', the former line being below thebottom of the jacket 503 and thelatter above the bottom of container505. This boiler 501 forms part of a single turn secondary,

boiler 501 is upright and loweset level of 47, to fapoint the circuit ofwhich is completed through copper bar 501x which is oflow enoughresistance to practically short circuit the rest of the system. hesecondary `is energized by primary coil 501e controlled'by switch 541.

The container 505, jacket 503, vapor supply tube ,502, gauge 539, vaporoutlet tube 512, down-flow tube 512 for the condensate, supplementalcondenser 524, `and return pipes 513a and 514 may be the same as inpreceding figures. For convenience there is preferably a glass gauge 555connecting pipes 502-514 for indicating the level of the mercury in thesystem.` In this system the pressure controlling valve 530 is located inthe pipe 512a between the jacket 503 and the condenser 524 and, asdiagrammatically indicated,it is adapted to be set for pressures aboveor below atmosphere. v,The exhaust pumpA is beyond the condenser andconsists of a well-known formof barometric dicated by 47',

jet condenser comprising the upwardly eX tending suction tube 525 forthe vapor, discharging downwardly through the jet 510"L in chamber 510supplied with water through opening 510b controlled by valve 510C.chamber connects with downwardly extending tube 529 which is preferablylong enough to altord a barometric column when water is the fluid. Thepipe 529 has an outlet at 550 below the level ot' the liquid incontainer 551. This container has two wateroutlets, one 552 to drain ofiwater when themercury level is at 47, 47, and the other 583, when it isat level 47', 47. The mercury vapor is condensed by the water andsettles out in the container 551.- It'rnight be returned Vto the systemthrough abarometric U-tube, but as shown there is a hand operated valveat 554 which is opened nal pressures are suitable. for in-low of mercurywithout ment of the apparatus.

In the systems of Figs. V3. and 5, where a This disturbing `of theadjustably is maintained in contact with the lower portion of thecontainer which is being heated by condensation ot the mercury vapor,there is special advantage in employing a vertically arranged propellerto alford vertical circulation ot' the mixture, and I have shown forthis purpose a. screw propeller 7() on the lower end ol' vertical shaft7l journalcdin the cover 506 and power driven through any suitablemeans, as for inst-ance, a beveled gear 7 2 driven by gear 73 on sha-tt74 which is supported in a bearing 75 and may be rotated from anydesired source ot power diagiaminatically indicated by belt pulleys 7 G,7 7, one o't which may be an idler while the other is keyed to saidshaft 74.

The vertical circulation thus provided is iml portant not only formixing but also for driving hot mixtures int-o cooling relation with theliquid mercury for boiling the latter during exothermic reactions andalso for displacing the cooler material upward in heating relation withthe condensing area of the container when the operation is endothermic.

t will be understood that the presence ot liquid mercury in bathingcontact with the same container which is heated by condensation ot hotvapor supplied from an outside source, is of great importance, not onlyfor cont-rolling the temperature during desired exothermic reactions,but also as an everpresent refrigerating medium which will automaticallycome into rperation as 'a safety appliance in cases where undesiredexothermic reactions may occur by accident as in case of certainimpurities in certain mixtures or in case of faulty regulation by thepressure controlling devices. t

A not uncommon case is where there'is a small amount ot' impuritycapable o t oxidizing or other exot-hermic reaction within the range otthe desired operating temperature. In such case the retrigerating actionof the boiling mercury will be sutiieient to keep down the temperatureiint-il the exotherniic reaction has been completed, after which .theprocess will proceed as before. In other cases as where the amount ofmaterial for the exothermic reaction is considerable, it may benecessary to have expert attendance and regulation to completely takecare of t-lie situation. Even in cases where the danger neverinaterializes, the advantage ot the liquid mercury as a precautionarysafety device is obvious.

It will be understood as to all ot' the systems shown herein thatadjustment of heating current may be such as to boil mercury at ratessuiiicient to supply more vapor than will be condensed in the heatingcoil or jacket. Such excess represents `waste but unless maintained thesystem will operate only with upper limit regulation. It, however, thevapor is always in excess, the working temperature will be kept up tothe predetermined limit as well as prevented from falling below it.

While the various systems disclosed herein are capable of being operatedeither above or belowatmosphere, as heretofore explained, there aregreat advantages in em- .ploying them for the operations which can beperformed at or below atmospheric pressure, that is, for temperatures ator below 3570 centigrade, the atmospheric boiling' point of mercury.Hence, as will be evident, a great variety of heating operations,particularly for chemical reactions can be accomplished with thepressure valve, 230 or 530, set to blow at or below atmosphere. In thebelow-atmosphere operation there can be no leaks of mercury to theexterior. Any leaks must be inward into the system and any impuritiesthus introduced are drawn off with the excess uncondensed vapor and aregradually worked out ot' the system by continued operation of thevacuumizing pump. l/Vhile the leaks are thus in the direction of safetyas regards human life and are taken care of as above described, it is tobe understood that they are highly undesirable and the greatest possiblecare is taken to prevent them.

In my prior application irst above mentioned I have stated that mercuryvapor may be obtained at 4300, Fahrenheit, under a pressure of onlynine-tenths pound to the square inch. Higher degrees of heat may beobtained with corresponding increase in pressure. I have also describedhow these pressures, required for desired temperatures, can bemaintained by a vacuum pump operated and controlled in the usual mannerin connection with an ordinary pressure gauge which indicates the boilerpressure. l-Vhile the inventions claimed in said application Serial No.553,640 canbe practiced by manual control of the pump in connection withthe gauge2 there are important advantages in employing automatic meansfor the purpose. Hence my present application includes certain varietiesof automatic meansv which may be used for controlling internalpressures. Also said automatic means include devices that are capable otoperation for above-atmosphere as well as belowatmosphere pressures.Specifically considered, the principal regulating means are in the`nature of relief valves and, to take care of the specific case where theinternal pressures, the pumps may be cut off either by hand valves asindicated in Fig. 3, `or by any desired automatic mechanism. Y

It will be understood thatk the pressure relief valve, such as 530, isdiagrammatically indicated as having the internal pressure on the valveelement directly opposed by external atmospheric pressure the externalpressure being adjustably decreasedh or increasedby the weighted lever.It will be understood, however,that I may employ' below that in thepipes leading from the condensers and it will sometimes be neces- 'saryto make allowance for this.

In this same connection it may b e noted that the condensed mercury maybe regulated. to a desired higher level than the mercury in the boilerby throttling the return flow of the condensed vapor. For instance, inFig. 5 the mercury may be raised to or above the level HL-47 in thecondensing` jacket while the mercury in the boiler is at a much lowerlevel by suitably adjusting A valve 570 Which can be inserted in pipe51.2.

Also the back pressure could be increased by partially closing a valvewhich can be arranged in pipe 502, like 102, Fig. 3. Preferably,however, the back pressure should be kept as small as possible so thatthe pressure throughout the entire system may be more nearly uniform.

In all of the systems shown herein the region which is to be primarilyheated to a predetermined temperature and which in operation has a bodyof hot condensate maintained in heat absorbing relation thereto, isindicated as a very simple form of container which must be partially orWholly recharged from time to time and the charge to be operated upon isindicated as a liquid. It will be understood, however, that the heattransfer methods and their application 'to the operations beingperformed in or upon the mixture, may be the same, or at leastequivalent, when the container 1s designed or equipped -for a continuousprocess, one

or more materials being continuously supplied in predeterminedquantities;I also where one or more ofthe materials are primarily solidseither remaining such or adapt-ed to become liquid or gaseous; orliquids, either remaining such or adapted to vapors and sublimates inall of the various physical forms and states of matter for which -heattransfer at high temperatures may be necessary or desirable. Thev prelferred methods cover temperatures ranging from just below the lowest redheat of lron down to the minimum vacuum boiling point vof mercury, andparticularly where close temperature regulation vWithin a very narrowrange is necessary or desirable, and particularly where the heattransfer is with aol reference to a material 0r materials requiringinitial heat application to be followed automatically by heat absorptionwhen a predetermined temperature is exceeded. In the latter class isobviously included the cases where the heating to a predetermined hightemperature produces an exothermic chemical'reaction, the sensible heatof which must be absorbed to keep down temperature.

I claim:

1. The method of transferring heat which consists in imparting heat tomercury to boil oil mercury vapor in one region of a circulating system,absorbing heat from the mercury vapor at another region of the system tocondense mercury; maintaining a body of condensate in heat absorbingrelation to the latter region; and governing the temperature bygoverning the internal pressure of the condensing vapor.

2. The method specified by claim 1, and wherein the predeterminedinternal pressure is below atmosphere and a partial vacuum is maintaindin the region to which the pressure is vented.

'l`l1e method of transferring heat which consists in imparting heat tomercury to boil ou' mercury vapor in one region of a circulating system,absorbing heat. from the mercury vapor at a second region ot' the systemto condense said vapor mercury, condensing surplus vapor in a thirdregion, and governing the temperature in the said second region bygoverning the internal pressure on the condensing vapor and by alsomaintaining a body of hot liquid mercury in heat absorbing relation to'said second region adapted to boil automaticall Y when said secondregion exceeds a pret etermined temperature.

4. The method of limiting the temperature of a hot body ifv and when itstemperature exceeds a predetermined limit, which method consists inmaintaining in heat absorbing relation thereto a body of hot liquidmercury, liniiting the pressure on said mercuiy to determine its boilingpoint at said limiting temperature, thereby automatically boiling saidmercury by the heat of said body when the latter exceeds'said limit, andlimiting increase of said pressure and boiling point by condensingthe'mercury vapor at a remote region cooled by an independent medium.

5. The method of conducting reactions requiring heating of the materialto a predetermined hi h temperature range and resulting in exot ermicreaction, which method consists in applying heat toboil mercury ina'closed conduit system, condensing the mercu vapor in heating relationto the materia regulating'the heating temperature by regulating thepressure of the vapor in the system at the condensation point andsimultaneously maintaining a body of hot condensate in heatl absorbingrelation to the mixture to be boiled by the latter when the exothmericreaction takes place and limiting increase of lnternal pressure andboihng point by condensing the mercury Vapor at a remote region of thesystem by applying an independent cooling medium in heat labsorbingrelation thereto.

6. The'method for control of temperatures i 4of operations Vor reactionsrequiringa limited range of high temperatures, producing or likely toproduce exothermic reaction in the Vmaterial so heated; which methodconsists in maintaining a supply o f liquid mercury in heat absorbingrelation to the material operated upon; hea-ting said material toy thedesired high limit temperature in any desired said limit and when saidboi ing occurs,

conducting the mercury vapor to anexterior region, there condensing itby an independentu cooling medium and utilizing the condensate tomaintain said supply of liquid mercury in said heat absorbing relationto the material being operated upon.

Signed at New York in the'county of New f this 18th day York and Stateof New York of ApriL'A. D. 1922.

oRosBY F-iELD. l

